Nine-piece solenoid set for the ZF 8HP45, 8HP55, 8HP70 and 8HP90 mechatronic unit - fixes harsh shifts, flare and limp mode on BMW, Audi, Jaguar and Land Rover.
If your eight-speed automatic has started slamming into 2nd or 3rd, flaring between gears at light throttle, shuddering like the converter clutch is chattering, or dropping into a reduced-gear safe mode with a transmission warning on the dash, the electrical side of the mechatronic unit is one of the first places to look. This nine-piece set covers the solenoids that plug into the valve body of a first-generation ZF 8HP: the 8HP45, 8HP55, 8HP70 and 8HP90 found in BMW, Audi, Jaguar and Land Rover models, plus the Chrysler-built 845RE used in Ram, Dodge, Chrysler and Jeep vehicles. It is a budget-friendly way to renew every solenoid at once when the hard parts are still healthy.
The 8HP has no shift valves in the old sense. The transmission control module sits on the mechatronic unit and fires variable-force pressure regulators that feed each of the five shifting elements directly, plus line pressure and converter clutch control. Sonnax's solenoid identification chart for the Gen 1 valve body maps eight positions: the MV-1 park solenoid and seven EDS regulators, including EDS-7 for line pressure, EDS-2 for the converter clutch and EDS-1 through EDS-6 for the A, B, C, D and E elements. Because each regulator only owns one job, a tired coil or a worn solenoid seat produces a complaint tied to one function, such as a single bad shift, no lockup, or pressure problems in every gear.
Two failures on this transmission mimic a bad solenoid: a leaking mechatronic sleeve that lets pressure escape before it reaches the valve body, and worn valve bores that bleed off the pressure a good solenoid is trying to hold. Our ZF8HP valve body wear guide walks through how to tell them apart.
Start with codes and the software level. Several factory bulletins for the 845RE and 8HP70 fix harsh shifting with nothing more than a control module update. If codes point at a specific position, the Sonnax ZF8-ZIP booklet gives a bench spec of 5.0 ohms at 68 degrees F per solenoid with the circuit board removed, measured with a meter that applies less than 0.6 volts. A coil far outside that number is bad. A solenoid that reads in spec while the scan tool shows commanded and actual pressure drifting apart points at the valve body instead. The ZF8HP common problems and fixes article lays out the full order of checks.
This set is listed for the Gen 1 family only: 8HP45, 8HP55, 8HP70, 8HP90 and the 845RE. It does not fit the second-generation 8HP50, 8HP75, 8HP95 or 850RE. Sonnax documents that the Gen 2 solenoids use different caps and snout diameters and that the B and D positions swap between generations, so a Gen 2 valve body will not accept these. Some Chrysler, Ram and Jeep applications switched to Gen 2 starting in 2019, so check the valve body casting and separator plate code, or send us your year and VIN and we will confirm. Browse every ZF eight-speed part on the ZF 8HP collection page.
If the valve body bores turn out to be worn, a full remanufactured 8HP70 valve body with solenoids is the more complete fix.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Only if your unit is a first-generation 845RE or 8HP70. Some Chrysler, Ram and Jeep applications moved to the Gen 2 850RE, 8HP50 or 8HP75 starting in 2019, and those use solenoids with different snout diameters. Check the valve body casting code or send us your VIN before ordering.
No, but it usually makes sense. Every solenoid sees the same fluid and heat, and replacing the set means the module relearns all positions together instead of mixing worn and new coils. If you reuse any originals, put each one back into the exact bore it came from.
With the circuit board removed, each solenoid should read about 5.0 ohms at 68 degrees F. Use a meter that applies less than 0.6 volts. A reading well above or below that indicates a failed coil.
ZF LifeguardFluid 8 or LifeguardFluid 9 with no additives. ZF warns that other oils can cause shift problems or damage. Set the level with the engine running and the fluid between 30 and 50 degrees C.
No. This kit is the solenoids only. The sleeve, conductor plate and pan are separate parts, and a leaking sleeve should be replaced at the same time because it causes the same pressure-loss symptoms.
Clear the codes and let the transmission relearn. A scan tool with adaptation reset is helpful, but the module will relearn over a series of warm, light-throttle shifts. Expect shift feel to settle over the first few drive cycles.
